Mg2SiO4 liquid under high pressure from molecular dynamics

We use a flexible potential model to perform large-scale molecular dynamics simulations of Mg2SiO4 melt up to pressures of 24GPa and at temperatures between 2390K and 3200K. We find that thermal pressure and the Grüneisen parameter γ increase linearly with density, independent on temperature. γ increases from 0.5 at ambient pressure to 0.75 at 24GPa. While Si stays overwhelmingly in tetrahedral coordination, the coordination of Mg increases significantly under compression, from an average 5-fold coordination at room pressure to 7-fold coordination at 24GPa. Medium range order in Mg2SiO4 as expressed by X-ray and neutron structure factors change considerably with pressure, with features at low wave-vectors q sharpening considerably and shifting to higher q. Diffusivity of the atomic species in Mg2SiO4 decrease uniformly with pressure and are well described by an Arrhenius law. For viscosity η we find good agreement with experiments at room pressure, and predict a rapid increase with pressure.